There are gaps in the Interstate Highway system, where the roadway carrying an Interstate shield does not conform to the standards set by the Federal Highway Administration (FHWA), the body that sets the regulations for the Interstate Highway System. For the most part, the Interstate Highway System in the United States is a connected system, with most freeways completed; however, some Interstates still have gaps. These gaps can be due to unconnected segments of the same route or from failure of the road to fully conform to Interstate standards by including such characteristics as at-grade crossings, traffic lights, undivided or narrow freeways, or movable bridges (lift bridges and drawbridges).
True gaps
True gaps are where multiple disjoint sections of road have the same Interstate highway number and can reasonably be considered part of "one highway" in theory, based on the directness of connections via other highways, or based on future plans to fill in the gap in the Interstate, or simply based on the shortness of the gap. The sections are either not physically connected at all, or they are connected but the connection is not signed as part of the highway. This list does not include different highways that share the same number, such as the two different I-76s, I-84s, I-86s, I-87s, and I-88s, which despite appearances, were always intended as distinct highways and were never intended as a contiguous route.
Interstate 26
In North Carolina, Interstate 26 has a gap from Forks of Ivy to Asheville at exit 4A of Interstate 240. This is because not all of the parts in the gap were built to Interstate standards. As of November 2023, Interstate 26 is designated as Future I-26, US 19, and US 23. Construction on building this gap to Interstate Standards was scheduled to start in 2022.[2]
Interstate 49
Interstate 49 (I-49) currently has three sections: the original alignment from I-10 in Lafayette to I-20 in Shreveport, one from I-220 near Shreveport to Texarkana; and the third section from I-40 near Alma, Arkansas to I-470/I-435 south of Kansas City, Missouri. A bypass south of Bella Vista, Arkansas was completed in 2021, and existed initially as Arkansas Highway 549; the latter designation is now used on a short section southeast of Fort Smith that is several miles long. It is planned to be connected to an interstate with a project to construct a new roadway from Arkansas Highway 22 to Interstate 40 in Arkansas. I-49 from Fort Smith to Texarkana is still unbuilt. These gaps are expected to be eventually closed.
As of 2021, projects to connect these segments are in varying stages of development. Indiana is currently working to connect the Port Huron–Indianapolis and Martinsville–Evansville sections by extending I-69 north from Martinsville to the I-465 Indianapolis loop, with construction planned to be complete in late 2024.[6] Kentucky and Indiana expect to begin construction of the eastern bypass of Henderson and new Ohio River crossing, connecting the Mayfield–Henderson and Martinsville–Evansville sections, in 2022.[7] Kentucky has plans to upgrade the remaining section of the Purchase Parkway and work with Tennessee to reconstruct the current interchange at the south end of the Purchase Parkway in South Fulton, Tennessee to provide a free-flow connection to the existing U.S. 51 freeway to Union City, while Tennessee finished I-69 bypass of Union City.[8] It is currently designated as SR 690. A further bypass of Troy is proposed but not yet funded, which would complete a freeway-standard route from I-155 in Dyersburg to Henderson. Tennessee has deferred plans to complete the section between Dyersburg and Memphis to close the gap until the South Fulton–Dyersburg section is completed.[9] The section from Memphis to Houston is the least developed; as of 2021, Mississippi has no current plans to extend I-69 further south, and the states of Louisiana and Arkansas have not funded construction of their portion of the proposed route (via El Dorado and Shreveport) between Mississippi and Texas, other than a two-lane southern bypass of Monticello, Arkansas designed to be incorporated into I-69 at a later date. Texas has continued to fund projects to upgrade U.S. 59, U.S. 77, U.S. 281, and other routes that would eventually form parts of I-69 in South Texas and East Texas, including the I-69W/C/E spurs.
As of 2023, I-99 has two sections: one from the Pennsylvania Turnpike to just south of I-80, concurrent with US 220, and one from the Pennsylvania–New York state line north to I-86 in Corning, New York, concurrent with US 15. Much of the intervening route, including the entire US 15 section between I-180 in Williamsport and the New York state line, has been constructed to freeway standards but as of yet is not signed as part of I-99.
The signing of the intervening route as I-99 will be completed when the route is upgraded to Interstate standards, connecting the two segments of I-99.
Freeway gaps
Freeway gaps occur where the Interstate is signed as a continuous route, but part, if not all of it, is not up to freeway standards. This includes drawbridges where traffic on the Interstate can be stopped for vessels. This does not include facilities such as tollbooths, toll plazas, agricultural inspection stations, or border stations.
In urban and heavily developed areas, Interstates may travel along surface roads or have at-grade intersections with stop signs or traffic lights. This usually happens because the Interstate started construction after the land was heavily developed and buildings such as residences and businesses and other roads would have to be removed to allow a freeway to pass through. Additionally, more developed land would have to be cleared for space to build interchanges to connect the Interstate and surface streets. This situation is extremely uncommon as Interstates are usually built around cities or through them on pre- or lightly developed land.
I-516 downgrades to an expressway as it heads toward its eastern terminus. The expressway features a frontage road right turn and an at-grade intersection with Mildred Street close to the terminus at Montgomery Street and Derenne Avenue (SR 21) in Savannah, Georgia. Mildred Street southbound is closed by concrete barriers.
I-19 between North West Street and its southern terminus at West Crawford Street at North Sonoita Avenue, in Nogales, Arizona, consists of surface streets with traffic lights. The signage of this segment is intended to help direct traffic entering from Mexico to the nearest interstate.
I-70 uses part of US 30 along a surface road in Breezewood, Pennsylvania. Traffic traveling eastbound on I-70/I-76 must exit and travel a short distance on US 30 in order to continue south on I-70 heading to Hancock, Maryland. (The routing is similar for traffic following I-70 in the opposite direction: traffic traveling north on I-70 must exit and travel a short distance on US 30 in order to continue west on I-70/I-76 or to enter the Pennsylvania Turnpike.) This is one of very few instances of traffic lights on an Interstate. There was formerly a sign of a policeman pointing at drivers leaving the Pennsylvania Turnpike to enter US 30, saying, "You! Slow Down!" Local businesses have lobbied to keep the gap to avoid a perceived potential loss of business.[11]
Several Interstates in rural areas of the U.S. have minor at-grade intersections (including median breaks) with farm access roads or authorized vehicle-only driveways used for highway maintenance or connection to nearby utility stations. This is usually due to the lack of an old highway, the need to provide access to property that was accessed via the road prior to its upgrade to an Interstate, and the high cost to construct an interchange for the small amount of traffic that would use such a connection or to build a frontage road parallel to the freeway to the nearest interchange.
I-10 in Hudspeth County, Texas has at least fifteen at-grade intersections containing median breaks with minor dirt or gravel roads.
I-11 in Boulder City, Nevada has an at-grade intersection with an authorized-vehicle-only service road giving access to Buchanan Boulevard and the WAPAMead substation. An interchange replacing this has been considered.[13]
I-15 in Wheaton Springs, California (east of Mountain Pass) has several at-grade intersections with dirt roads, including one leading to a house.
I-15 west of Mesquite, Nevada has an at-grade intersection with Toquop Wash Road, a dirt road. Another access point to Toquop Wash Road passes under the I-15 southbound lanes and connects to the northbound lanes in the median.
I-15 southbound near Cove Fort, Utah has an at-grade intersection with Cinder Crater Road, an asphalt and gravel road that provides access for trucks to the Cinder Crater quarry.
I-520 in Augusta, Georgia has an at-grade intersection with a gravel and asphalt road that provides access to Lovers Lane.
I-40 in the mountains of western North Carolina has at-grade access to several dirt roads, as well as a partially grade-separated interchange that lacks ramps or RIROs where roads directly connect to the I-40 carriageways. (Example)
I-40 in western Texas has eight at-grade access points for cattle ranches with median breaks.
The northbound lanes of I-5 in Washington intersect with an at-level crosswalk approximately 100 feet (30 m) south of the border with Canada. This crosswalk allows pedestrians access to a monument that is part of Peace Arch Park.
Undivided and narrow freeways
Two-lane stretch of I-93 through Franconia Notch in New HampshireTwo-lane stretch of I-81 on the Thousand Islands Bridge crossing part of the Saint Lawrence RiverThe Mackinac Bridge, which carries I-75, has no hard shoulders, and has only a 4-inch-tall (10 cm) divider between the opposing directions
This section addresses two-lane freeways and other narrow or undivided freeway sections of the Interstate, excepting instances of continuing routes using one-lane ramps and merge leads. Narrow gaps between opposing directions with jersey barriers taller than four feet (1.2 m) are excluded from this section; therefore the separation criterion is really either a 4-foot-tall (1.2 m) wall, or a 100-foot-wide (30 m) median, whichever is greater.
I-40's western 15 miles (24 km) in North Carolina in the Harmon Den Wildlife Management Area has several S-curves, a Jersey barrier with extremely narrow left shoulders and a few at-grade intersections albeit in RIRO style.
I-55 enters Tennessee from Arkansas on the Memphis and Arkansas Bridge, which itself merits mention as a narrow through truss bridge. Just east of the bridge I-55 transitions from its east–west river crossing to the north–south alignment heading toward Jackson, Mississippi. There is an interchange that forces through I-55 traffic to enter and exit in an old cloverleaf; in 2015 improvements were announced but are stalled. The improvements to the I-55 / Crump Boulevard interchange will be accomplished by constructing new through travel lanes for mainline I-55 traffic, which will eliminate the requirement for interstate traffic to use single-lane, low-speed ramps in order to continue on I-55. A new multi-lane roundabout intersection will be constructed to replace the existing cloverleaf interchange and provide improved access to and from I-55 and existing local roadways.[15]
I-555 at its southern terminus through the I-55/U.S. 61/AR 77 interchange becomes a two-lane undivided highway for 0.34 mi (0.55 km).
Interstate 70 is one-lane only in these following locations:
The Mackinac Bridge, which carries I-75 over the Straits of Mackinac between St. Ignace and Mackinaw City, Michigan, has no wide median or hard shoulders due to space constraints. Nor does it have a Jersey barrier; instead, it has either a 4-inch-tall (10 cm) yellow divider between the opposing directions (where the inner lanes are a metal grate) or a flat double-yellow line (where the inner lanes are paved). The speed limit is also reduced to 45 mph (70 km/h) for cars and 20 mph (30 km/h) for trucks. The highway returns to Interstate standard for about 50 miles until it reaches the Sault Ste. Marie International Bridge, which carries undivided lanes to the Canada–US border in the middle of the bridge, where I-75 terminates.
I-93 is a two-lane divided parkway, or a "super two", through Franconia Notch in New Hampshire. A four-lane Interstate Highway was once proposed here, but the concept was abandoned because of environmental concerns, in part because of vibrations that could harm the Old Man of the Mountain rock formation (which collapsed in 2003 regardless). This section of highway was for many years marked as US 3 and "To I-93", but these have now been replaced with regular I-93 signs. The Federal Highway Act of 1973 exempts this 7.6-mile (12.2 km) stretch from the Interstate Highway standards that apply elsewhere, and this highway is considered to be I-93 for all practical purposes.[17] This section of I-93 in New Hampshire is now the only remaining multi-mile section of two-lane freeway on an Interstate Highway in the United States.[citation needed] In addition, parking along portions of I-93 through Franconia Notch was permitted until early 2019 when barriers and signage were posted due to safety concerns.[18]
Some stretches of Interstate highway use a barrier transfer machine on some bridges to convert inner lanes from one direction to the other, where it would be too costly to upgrade/rebuild to a higher-capacity bridge. In any case the traffic distribution is strongly asymmetric depending on the hour of the day. This kind of bridge typically contains undivided lanes without the flexible Jersey barrier that is manipulated by machines.
By Interstate standard, all bridges on the Interstate system must be fixed as to not interrupt the flow of traffic. Several bridges on the system, however, are movable:
I-95/I-495 pass together as the Capital Beltway over the Potomac River on the Woodrow Wilson Bridge, a double-leaf bascule span. Even though the original bridge was replaced in the 2000s, the new bridge also has a draw span, albeit with more vertical clearance resulting in fewer openings than the old bridge—about 65 per year, an average of about one every six days.
I-695 has a drawbridge over Curtis Creek, south of Baltimore and just west of the Francis Scott Key Bridge. This section of the Baltimore Beltway is not part of the Interstate Highway System, however, and is officially Maryland Route 695 despite the Interstate signage on the highway.[25][26]
Freeway-to-freeway crosspaths without direct connection
I-271 in Ohio lacks a direct interchange with the I-80 section of the Ohio Turnpike; traffic interchanges between the two via I-77 and Ohio State Route 8, which both pass nearby.
I-475 has no direct interchange with I-80/I-90 on the Ohio Turnpike near Toledo., though there is an indirect connection via US 20 and Dussel Drive.
I-476 does not have a direct interchange with I-78 in Lehigh County, Pennsylvania, though there is an indirect connection via US 22 and PA 309. Additionally, while it connects directly to I-80, the freeway-grade is disrupted when the ramps intersect PA 940.
The Massachusetts Turnpike (I-90) passes over I-391 without interchange in Chicopee, Massachusetts. The overpass is about one mile (1.6 km) north of the I-391 southern terminus at I-91, and approximately 1.4 miles (2.3 km) from the Mass Pike interchange with I-91 and US 5.
I-295 passes over I-276 without direct interchange in Bristol Township, Pennsylvania, though an interchange is under construction that will provide direct connection.
I-99 has connection gaps with both I-70/I-76 and I-80 in central Pennsylvania, both through at grade roads near Bedford and Bellefonte, Pennsylvania. The latter is expected to become freeway-grade as part of I-99's aforementioned northern extension.
Proposed
I-422 (proposed) would have no direct freeway connection to its parent I-22, though the two routes would cross near Adamsville, Alabama.
Connection gaps
Auxiliary Interstates (also known as three-digit Interstates) are intended to connect to their parent either directly or via a same-parented Interstate (like I-280 in California being connected to I-80 via I-680). Often, these connection gaps occur to eliminate concurrencies between other three-digit routes. Freeway gaps (signed or unsigned) that officially connect auxiliary routes to the parent are excluded.
Current examples
I-210 in California does not currently connect directly to I-10 or any of its spurs according to freeway signage. It was signed all the way to I-10 until 1998, when California State Route 57 replaced the portion of I-210 through Covina and San Dimas to provide a proper connection to current State Route 210. The former portion of I-210 now known as SR 57 still remains on the Interstate Highway System federally defined as Interstate 210[27] maintaining its connection to I-10, but it is not signed as per Caltrans tradition to sign state highways by their state definition over their federal definition. State Route 210, built as an extension to replace Route 30, connects to I-10 further east in Redlands, and California is petitioning to have that portion signed as I-210 as well. When that happens, this gap will close.[citation needed]
I-238 does not have a parent. It was previously a part of California State Route 238 that was built to Interstate standards, and it was added to the Interstate system using the same number it had as a state highway. It was upgraded to be an auxiliary route of I-80, but no three-digit combinations were available at the time the route was designated an interstate. Additionally, the exit numbers continue the mileage from the state highway instead of starting over from 1.[28]
Due to Highway revolts in New York state forcing the interstate to terminate prematurely, none of the spurs of I-78 in New York City (I-278, I-478, I-678, I-878) connect to the parent road I-78, nor is there any surface street with a state route designation with the same number that continues with a solid connection. I-78 was planned to extend southeast through New York City via the Lower Manhattan Expressway, Williamsburg Bridge and Bushwick Expressway, then east along what is now I-878 and north along what is now I-295. I-78 would have then split into two branches (the current I-295 and I-695), which would have both terminated at I-95.[29][30] I-478 comes the closest, and would have intersected I-78 as part of the Westway project;[31]: 10 this project was later canceled.[32] I-278, the only I-78 spur to leave New York City, was planned to extend northwest to I-78 at Route 24.[33] Since all the spurs are interconnected, only one of them needs to be eventually connected to its parent route for all of them to conform to numbering standards.
I-585 in South Carolina currently does not connect directly to I-85. Until 1995, I-85 was routed along present-day I-85 Business. In that year, I-85 was moved to the north to bypass Spartanburg while I-85 Business took over its former route, leaving I-585 without a connection to its parent route until upgrades to the existing US 176 highway are complete.[34]
As of July 2022, I-587 in North Carolina does not connect with its parent route, I-87. Upgrades to the existing US 264 freeway from US 64 to I-95 to Interstate standards, as well as extending I-87 via upgrades to US 64, will connect I-587 with its parent route.
I-335 in Oklahoma will not have a connection with its parent route, I-35, until an extension of the road to Purcell is built.
Numerous three-digit Interstate routes are unsigned on some portions, leading some to think there are connection gaps. These so-called connection gaps do not have internal unsigned concurrencies on other Interstate highway segments between the "parent route" and signed terminus.
^Special Committee on U.S. Route Numbering (May 19, 2012). "Report to SCOH"(PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. Archived from the original(PDF) on June 3, 2019.
